I would vehemently disagree, Andinoacara generally prefer temperatures in the low and mid 70s F. Most of these species are found in Ecuador, Peru, and Colombia, where the rivers start high in the mountains. The water temperatures in these regions are not the steamy 80s of the Brazilian lowlands. Most of the species often sold as "Blue Acara" are quite comfortable in the mid to low 70s, as are the rivulatus complex. I can't source the exact temperature ranges, but the higher the altitudes where they live, the cooler the temperatures are going to be. There are also a number of true Aequidens and closely related species that do live in the lowlands, and they would require the warmer temperatures.
South America is not one big flat land mass with the same environmental conditions over the whole place. There are actually temperate Cichlids in the southern countries that require a cooling into the 50s F to remain healthy. Making broad statements like "their comfort zone is 78-84F" is careless, at the very least, and misleading at the worst.
I second Mr. Chromedome... A lot of the books cite the collecting temperatures during the middle or hottest part of the day. While water is a better thermal insulator than air, it will still vary in temperature over the course of 24 hours, and be much cooler at the coldest part of the night than it is at the hottest part of the day. Seasonal changes will produce even greater swings in the extremes.
I know of quite a few people who keep their south american fish in unheated tanks in their living space (i.e. they are not turning up the heat in the room to the low 80's either).